This invention relates generally to burner assemblies and, more particularly, is directed to a register for a burner assembly.
Burner assemblies in which gas, oil, coal and other combustible materials are mixed with air are well known in the art. Such burner assemblies are generally associated with industrial boilers and furnaces, and comprise a structure known as a register which is usually mounted at the base of the furnace or boiler, and which contains appropriate fuel and air inlets, and houses the burner gun that serves to ignite the fuel. Thus, the combustible material, such as oil, coal and gas, enters the register through appropriate inlets formed in the register. In order to provide efficient mixing of the air with the fuel, a plurality of entry ports are generally positioned within the annular side wall of the register, such that the air impacts the combustible material at an angle thereto so as to provide enhanced mixing. Additionally, the entry ports within the annular side wall may be inclined so as to provide a tangential spin to the air supplied to the register.
With such conventional arrangement, the problem of adequate mixing of the air with the combustible material still remains. In other words, it is still desirable to obtain more effecient and effective mixing of the air and fuel.
Related to this problem of inadequate air balance, that is, inadequate mixing of the fuel and air, there is the problem of reducing nitrous oxides (hereinafter referred to as NOx), resulting from oxidation of nitrogen in the air, which, in turn reduces the flame retention, thereby providing for lowered radiation.
As discussed in U.S. Pat. No. 4,297,093, various methods have been used for suppressing the generation of NOx, such as reduction of the flame temperature, reduction of oxygen concentration in the combustion zone and shortening of the stay time of the combustion gas in the combustion zone of high temperature. However, as described therein, the adoption of these techniques also poses various problems concerning stability of the flame, emission of unburnt substances and smoke, responsive characteristic to the fluctuation of load, thermal efficiency, the cost of modification of the boiler, increase of the fuel consumption, and the like. U.S. Pat. No. 4,297,093 discloses an arrangement for reducing NOx by utilizing a swirler to provide a small scale of turbulence to the combustion air. The swirler is located in the vicinity of the fuel injection port.
Related to the turbulence discussed above, it is known that the flow velocity of a combustible mixture is reduced when an obstacle is placed in the flow path thereof. Accordingly, the chances for the flame speed to match the flow velocity at some region in the flow field, a requirement of flame stabilization, are improved. If the obstacle is a bluff body, that is, a non-streamlined body, as the fluid is accelerated, a flow velocity is reached where the adverse pressure gradient downstream from the obstacle is strong enough to set up a recirculating vortex system in the wake of the bluff body, as taught by Combustion Aerodynamics, J. M. Beer and N. A. Chigier, Halsted Press Division, John Wiley and Sons, Inc., New York, pages 68 and 73.